PROJECT SUMMARY Salmonella enterica is a significant cause of morbidity and mortality throughout the world. S. enterica causes acute gastroenteritis and is also responsible for systemic diseases that result in fatal infections. Salmonella infection presents as intestinal outgrowth, penetration of the epithelial barrier, and subsequent uptake by macrophages, where Salmonella is ultimately trafficked to secondary lymphoid organs such as the spleen. S. enterica encodes two type three secretion systems encoded in the Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2) that are essential for cell invasion and intracellular survival, respectively. Regulation of virulence traits is an essential strategy for bacterial pathogens to cause disease. Ethanolamine is an abundant metabolite in the gastrointestinal (GI) tract and is also present in the intracellular environment. In the GI tract, the bacterial transcription factor EutR promotes expression of genes encoding ethanolamine metabolism, which enables S. enterica to utilize ethanolamine as an energy source and establish infection. During later stages of infection, EutR activates expression of SPI-2 to enhance S. enterica survival within macrophages, and thus promote dissemination. Although EutR is important for S. enterica disease progression, very little is known about EutR regulatory circuits operative during infection or how these regulatory circuits influence S. enterica interaction with the host. In Specific Aim 1, we will perform a detailed characterization of the role of EutR-dependent gene regulation in modulating host responses. In Specific Aim 2, we will elucidate EutR-regulatory circuits operative during infection that influence disease outcome. These studies are important to developing new strategies to treat infectious diseases.